The invention relates to an improvement of a bending tube used in an endoscope.
An endoscope is designed for insertion of its distal end portion into internal organs of a human body such as stomach or intestines so that the condition of a part to be examined may be visually observed through an observation window formed in the distal end portion and an eyepiece assembly mounted on a control unit which remains outside the human body. The control unit and the distal end portion are interconnected by a flexible tube which includes a bending tube at its juncture with the distal end portion. It is not intended that the flexible portion or tube be positively controlled for bending by an operation of the control unit even though it is free to flex along the curved walls of the internal organs. By contrast, the bending tube is subject to a two- or three-dimensional bending by an operation of the control unit in order to swing the distal end portion so that the observation window therein may be easily directed toward a part to be examined.
It is necessary that the bending tube houses a number of internal components such as optical fibre bundles and/or forceps conduit internally, and this requires that the bending tube be as simple and thin a structure as might be desired and have a satisfactory bending strength.
Most conventional bending tubes comprise a framework covered with a braided work which is in turn covered with an outer shell. Such structures often caused accidents whereby the framework may damage the braided work or outer shell or even pierce therethrough. In addition, a conventional bending tube is thick-walled resulting in a decrease in the internal space available, and is also limited in the degree of bending because of the tube structure.